Electromagnet switching devices such as solenoids are used in any number of applications, ranging from automotive engines and industrial valve systems, to generators and consumer products. Solenoids are typically electromechanical devices that convert an electrical energy input into to a linear mechanical motion output. Solenoids typically have an inductive electromagnetic coil that is wound in such a manner to define a hollow core portion wherein a metal plunger or armature is situated. The coil is typically wound around a plastic bobbin or other non-magnetic material formed into a bobbin. When a current is applied to the coil, the winding creates a magnetic field which acts upon the plunger, causing the plunger to reciprocate between a first and second position. In most instances, the magnetic field draws the plunger inward to a retracted or energized position towards a stop that limits its travel. The plunger provides the linear mechanical force that is employed to move an external load a predetermined distance. Solenoids are generally constructed having either a single coil or dual coils. The coils are typically copper, but other materials may also be utilized.
Although the forces generated by the coil are relatively weak over long distances, they are often adequate or even considered strong over short distances. They do, however, typically exhibit excellent speed and reaction time. Pneumatic valves or mechanical linkages, as non-limiting examples, are prime candidates for mechanical devices that utilize the linear motion produced by solenoids.
As is well known in the art, the force applied to the plunger is proportional to the change in inductance of the coil with respect to the change in position of the armature, and the current flowing through the coil. This is illustrated by Equation (1), which indicates, as a merely illustrative example, that a change in magnetic flux/unit time through a coil of wire induces an EMF in the wire:
                    ɛ        =                              -            N                    ⁢                                    d              ⁢                                                          ⁢              Φ                                      d              ⁢                                                          ⁢              t                                                          (        1        )            
Where:
ε=induced EMF;
N=number of turns in the coil; and
Φ=magnetic flux.
When a single coil solenoid is energized, the current induced must create a magnetic field that is sufficient to not only actuate the plunger, but also to maintain the plunger in an energized position.
As noted, there are a number of applications for electrically actuated solenoids, many of which subject the units to hostile environments. For example automotive, marine, and numerous industrial applications subject solenoids to particulate matter, large temperature swings, and moisture. As moisture is particularly damaging for the electrical components found in a solenoid, water resistant solenoids have been developed to cope with such environments. In one prior art example, coil components are completely encapsulated in a potting, such as epoxy, thermo-setting plastics, or silicone rubbers. Unfortunately, by completely coating internal electrical components with potting, access to internals is compromised, such that it is not possible to insert tools into the solenoid during servicing. This is a significant drawback of water resistant solenoids, as the hostile environment in which they are deployed necessitates servicing at regular intervals. If openings in the solenoid outer housing that allow tools access to inner components are present, this provides yet another potential route for fluids to compromise the integrity of the device.
Therefore, there is a need for a solenoid having an improved construction such that solenoid service is easily facilitated, yet environmental sealing is not compromised. There is a need for a solenoid that can be easily assembled and disassembled at its service location without the risk of harming relatively delicate internal components or destroying its environmental integrity. Concomitantly, there is a need for a method of servicing a solenoid wherein environmental sealing is not compromised. There is additionally a need for a method to easily service a solenoid without the risk of harming relatively delicate internal components. The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide an apparatus and method relating to a solenoid having an improved connection between an external housing and internal solenoid components, thus allowing a user to apply external forces to the housing, for assembly and disassembly purposes, without damaging the internal structures or compromising the solenoid's environmental integrity.